THE PERFORMANCE OF THE NCEP OPERATIONAL MODELS FROM AN HPC PERSPECTIVE

8/12/98


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Table of Contents

THE PERFORMANCE OF THE NCEP OPERATIONAL MODELS FROM AN HPC PERSPECTIVE

Understanding the performance of the operational model is critical to being able to forecast the sensible weather

Why models have forecast problems

The way the physics are approximated can lead to model errors, for example

ETA MODEL IS BEST

ETA IS BETTER AT FORECASTING PRECIPITATION OVER COMPLEX TERRAIN

ETA MODEL TERRAIN OVER NORTHERN CA.

MORE ON ETA PERFORMANCE

ETA AND STORM TRACKS

COMMON ETA ERROR ALONG EAST COAST

NOTE THAT THE ETA SURFACE LOW IS A LITTLE WEST OF ITS 500 MB CENTER. THE NGM HAS A MUCH BETTER FIT TO THE 500 MB PATTERN.

THE LOW VARIES A LITTLE NORTH AND EAST OF THE NGM. REMEMBER, THE NGM IS TYPICALLY TOO SLOW WITH LOWS ALONG THE COAST.

VERIFYING PRECIPITATION

MODEL BIAS AND THREAT SCORE

Eta 12-24 Hr Bias (Forecast/observed) Using A Point Verification Dec 97-Feb 98

Eta 24-36 Hr Observed Bias Dec 97-Feb. 98

Eta 12-24 Hr Bias During August (Left) And Sept (Next Slide) 97

Eta Has A High Bias Across The South During The Warm Season

Regional ETA verification using model grid (80 km)

Regional ETA verification using model grid (80 km)

ETA .50 OR MORE PERFORMANCE DURING WARM SEASON

ETA PERFORMANCE FOR .50 OR GREATER AMOUNTS APR 96-NOV 97

Regional ETA verification using model grid (80 km)

Regional ETA verification using model grid (80 km)

ETA MODEL HAS PROBLEMS PREDICTING THE STABILITY.

WHEN HIGH SOIL MOISTURE IS PRESENT, OR WHEN THE MODEL FIRST GUESS THINKS THE SOIL MOISTURE IS HIGH,

WHEN LOW SOIL MOISURE IS PRESENT DURING SUMMER OVER THE HIGH PLAINS, ESPECIALLY WEST TX, THE FORECAST CAPE IS TOO LOW

WHEN SO MOISTURE IS LOW IN SUMMER IN THE PLAINS, THE SURFACE DEWPOINT IS TOO LOW AND THE TEMPERATURE IS TOO HIGH

Forecast vs. Observed Best Cape Spring 96

A NUMBER OF AVN/MRF PERFORMANCE CHARACTERISTICS HAVE CHANGED IN THE PAST YEAR.

AVN/MRF Often Have Problems Handling Upslope Events

About 75% of the AVN Rainfall Over the OK Panhandle Was Grid-scale Precipitation (Not Convection).

Another Case: AVN Wraps Low Too Far North And West. Both Surface and 500 mb Lows Are Too Deep.

Aviation Model handling of 500 mb trough

BIAS COMPARISON OF 12-36 HR MRF AND EARLY ETA FORECASTS

The MRF and MRFX spin-up precipitation bombs and tropical systems erroneously at all time ranges.

MRF PERFORMANCE FOR 3-5 DAY FORECASTS

MRF PERFORMACE (3-5 DAY) CONTINUED.

NGM AND THE SURFACE PATTERN

THE NGM AND AVN/MRF HAVE SERIOUS PROBLEMS WITH ARCTIC AIRMASSES

THE NGM LOWERS HEIGHTS TOO MUCH IN THE NORTHERN ROCKIES AND HIGH PLAINS

Why models have problems with arctic airmasses

LOWS TO THE LEE OF THE ROCKIES

NGM 12-36 Hr Winter Threat Score For .50 Or Greater Amounts

12-36 HR .50 OR GREATER NGM WARM SEASON THREAT SCORE

NGM .50 OR GREATER WINTER BIAS

THE NGM ALMOST ALWAYS SIGNIFICANTLY UNDERPREDICTS THE MAXIMUM

NGM WARM SEASON BIAS FOR .50 OR GREATER AMOUNTS

IN CONCLUSION

Author: NCEP user

Email: norman.junker@noaa.gov

Home Page: /research/res2.html

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